The finches of the Galapagos Islands, a major inspiration for Darwin's theory of evolution, are under threat from an introduced parasite. In a bitter irony, the animals most identified with natural selection may die out if they can't evolve fast enough. However, a new report suggests that human efforts to save these iconic birds could prove effective.
In the Journal of Applied Ecology, Professor Dale Clayton of the University of Utah used mathematical simulations to predict the effect the parasitic nest fly Philornis downsi is likely to have on the finches. The study "shows that the fly has the potential to drive populations of the most common species of Darwin's finch to extinction in several decades," Clayton said in a statement.
The parasitic fly lays eggs in the birds' nests so its larvae can drink the blood of nestlings. Few chicks raised in infected nests survive.
Although the speed with which Galapagos finches can evolve became clear when a new species appeared before other scientists' eyes, Clayton said: “The question is, will these finches have enough time to develop effective defenses before they are driven to extinction by the fly? It's an arms race.”
However, Clayton added that even “a modest reduction in the prevalence of the fly – through human intervention and management – would alleviate the extinction risk.”
Possible control methods include releasing sterile males to interfere with breeding, or introducing wasps that parasitize the flies within their native habitat but have yet to make it to the Galapagos. A more time-consuming approach would be to hand-rear chicks in fly-free nests.
The authors also suggest distributing cotton balls treated with pesticides, which the birds will collect and take to their nests, fumigating them in the process. The modeling indicated that a 40 percent reduction in fly infestation could buy the finches an extra 60 years, potentially enough for them to evolve their own defenses.
"Darwin's finches are one of the best examples we have of speciation," said Dr. Jennifer Koop, who did much of the research for the paper in the course of her Ph.D. "They were important to Darwin because they helped him develop his theory of evolution by natural selection." A single species of finch colonized the islands 3 to 5 million years ago, and has now diversified into 14 to 18 species (depending on classification) that are adapted to specific niches in the Islands' diverse environments.
The modeling was based on the medium ground finch, of which 500,000 are estimated to survive, using data from five years of breeding on Santa Cruz Island, the birds' main habitat. "In two of the three scenarios tested, our model predicted that medium ground finch populations on the island of Santa Cruz were declining and at risk of extinction within the next century," the researchers report.
Clayton noted that the danger to rarer finch species is likely to be higher still. Efforts to protect the finches may be enough to save the most common species, but prove insufficient to preserve the diversity that makes the Galapagos Islands so special.